A non-oriented electrical steel sheet is a steel sheet which a magnetic property thereof is uniform in all directions on a rolling plate, and is widely used in a motor, iron core of electric generator, electric motor, small transformer, and the like, and is used in demanding markets of driving motor, home appliances and large motor separately in two types such as one that a stress-relieving annealing (SRA) for improving the magnetic property after punching working should be practiced and the other that the SRA is omitted if cost loss is larger than the effect of magnetic property by the SRA.
A forming of the insulating film is a procedure which belongs to a finishing process for manufacturing a product, and requires a stickiness resistance that steel sheets of iron cores are not adhered to each other after the SRA which recovers the magnetic property by relieving the processing stress of the steel sheet and the continuous punching workability inhibiting abrasion of a mold, and a surface adherence, and the like, upon preparing iron cores by laminating many materials after the punching working in a predetermined shape, in addition to electrical properties inhibiting an occurrence of eddy current. In addition to said basic characteristics, an excellent application workability of coating solution, solution stability usable for a long period after the combination, and the like, are also required.
Meanwhile, a main purpose of a non-oriented insulating film resides in an inter-layer insulation between iron sheets to be laminated. However, as the use of small electric motor is increased, a film performance advantageous to a workability, weldabilty and corrosion resistance, as well as an insulating property is evaluated as a major physical property, and recently an electrical steel sheet having excellent surface quality is required as the surface quality of the steel sheet also has an effect on the use characteristics.
Also, the non-oriented electrical steel sheet is currently riding a wave of high-end by the development of high efficiency motor to keep pace with government's low-carbon policy and as it proceeds to the high-end, the surface of electrical sheet requires high functionability (high insulating property, high heat resistance, high corrosion resistance).
In particular, an excellent insulating property between the layers of non-oriented electrical steel sheets, which the performance of motor can be maximized by minimizing Eddy Current Loss, is an essential item.
In order to secure an excellent insulating property for the non-oriented electrical steel sheet, the method of increasing a coating thickness thereof is the most common method. However, if the coating thickness is increased, there is a disadvantage that the properties such as wettability, heat resistance, adherence before/after SRA and Stacking Factor, and the like, are deteriorated.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.